Barrier operators automatically move an access barrier, such as a garage door between open and closed positions. Typically, the open and closed positions of the access barrier are defined by the upper and lower physical limits of the access barrier. For example, the lower limit may be established by the floor upon which the access barrier closes. Whereas, the upper limit may be defined by the highest point the access barrier will travel, which can be limited by the operator, a counterbalance system provided by the barrier operator, or the physical limits of the access barrier's track system. The upper and lower limits are employed to prevent damage to the access barrier that may result from an attempt by the barrier operator to move the access barrier past its physical limits. Under normal operating conditions, the limits of the barrier operator may be set to match the upper and lower physical limits of the access barrier. However, the barrier operator limits are normally set to a point less than the physical upper and lower limits of the access barrier to minimize wear.
Systems used to set operator limits are composed of switches used to terminate travel in the up and down directions. These mechanical switches, which have a limited life span, are adjustable and can be used by the consumer or an installer to “fit” the access barrier travel to a garage opening. Metal fatigue and corrosion are the most likely causes of switch failure. Another drawback of mechanical switches is that they can be wired in series with the motor, which creates high current draw across the switch contacts causing failure. A further limitation of limit switches is that the up and down limits, which must be set manually, can be improperly set or misadjusted.
Other position limit systems employ pulse counters that set the upper and lower travel of the access barrier by counting the revolutions of an operator's rotating component. These pulse counters are normally coupled to the shaft of the motor and provide a count to a microprocessor. The upper and lower limits are programmed into the microprocessor by the consumer or installer. As the access barrier cycles, the pulse counter updates the count to the microprocessor. Once the proper count is reached, which corresponds to the count of the upper and lower limits programmed by the consumer or installer, the access barrier stops.
Prior to being operated, a barrier operator is often configured by its manufacturer to move the access barrier at a predetermined speed. This predetermined speed is established, generally, by setting the amount of output power that is supplied to the drive motor of the barrier operator. However, during the movement of the access barrier resistance is often encountered that decelerates, or slows the movement of the access barrier. Resistance may occur due to a variety of causes, including debris on the track of the access barrier, lack of lubrication between the access barrier and the track, or the gradual wear of the mechanical components that comprise the access barrier and barrier operator. Furthermore, the weight of the access barrier may also serve to amplify any resistance encountered by the access barrier (more so in the upward movement than in the downward movement of the access barrier). Conversely, the movement of the access barrier may be accelerated, should the access barrier encounter a lack of resistance, or if the barrier operator moves from a position of substantial resistance to a position having reduced resistance. Because of the aforementioned acceleration and deceleration, the access barrier may move in a non-uniform, or disjointed manner, rather than in a fluid manner commonly associated with access barriers. As a result, additional stress is placed on the barrier operator, access barrier, and any supporting structures utilized thereby. Additionally, as the barrier operator, access barrier and other supporting structures wear after extended use, the unwanted acceleration/deceleration may become worse.
Typically to overcome the problems associated with the acceleration/deceleration of the access barrier, a system that samples the speed and position of the access barrier in real-time may be employed. By taking samples, the amount of power supplied to the motor of the barrier operator may be decreased or increased if the sampling system detects that the access barrier is respectively accelerating or decelerating at various points throughout the access barrier's movement. However, because the instant system attempts to make the adjustment to the motor power in real-time, overshoot, undershoot, or possibly oscillation in the speed of the access barrier may occur. As a result, a disjointed movement of the access barrier may still occur.
Therefore, there is a need for a constant speed barrier operator that adjusts the amount of power supplied to the motor at the end of an access barrier's movement, so as to provide a constant and uniform access barrier movement. Additionally, there is a need for a constant speed barrier operator that samples the movement of the access barrier, and adjusts the amount of power delivered to the motor of the barrier operator after each cycle of the access barrier's movement. Still yet, there is a need for a constant speed barrier operator that does not create overshoot, undershoot, or generate unwanted oscillation of the access barrier. Furthermore, there is a need for a constant speed barrier operator that utilizes phase control to control the speed of the motor of the barrier operator.